The present invention generally relates to emergency oxygen supply systems such as are routinely carried on commercial aircraft for deployment upon loss of cabin pressure. More particularly, the invention pertains to enhancing the efficiency with which the supplied oxygen is used to thereby reduce the total amount of oxygen that needs to be carried on an aircraft.
Emergency oxygen supply systems are commonly installed on aircraft for the purpose of supplying oxygen to passengers upon loss of cabin pressure at altitudes above about 10,000 feet. Such systems typically include a face mask adapted to fit over the mouth and nose which is released from an overhead storage compartment when needed. Supplemental oxygen delivered by the mask increases the level of blood oxygen saturation in the mask user beyond what would be experienced if ambient air were breathed at the prevailing cabin pressure altitude condition. The flow of oxygen provided thereby is calculated to be sufficient to sustain all passengers until cabin pressure is reestablished or until a lower, safer altitude can be reached.
Each such face mask has a reservoir bag attached thereto into which a constant flow of oxygen is directed upon deployment of the system and upon activation of the individual face mask via a pull cord. The oxygen is supplied continuously at a rate that is calculated to accommodate a worst case scenario, namely to satisfy the need of a passenger with a significantly larger than average tidal volume who is breathing at a faster than average respiration rate when cabin pressure is lost at maximum cruising altitude. A total of three valves that are associated with the mask serve to coordinate flows between the bag and the mask, and between the mask and the surroundings. An inhalation valve serves to confine the oxygen flowing into the bag to the bag while the passenger is exhaling as well as during the post-expiratory pause and at all times also prevents any flow from the mask into the bag. When the passenger inhales, the inhalation valve opens to allow for the inhalation of the oxygen that has accumulated in the bag. Upon depletion of the accumulated oxygen, the dilution valve opens to allow cabin air to be drawn into the mask. The continuing flow of oxygen into the bag and through the open inhalation valve into the mask is thereby diluted by the cabin air that is inhaled during the balance of the inhalation phase. During exhalation, the exhalation valve opens to allow a free flow from the mask into the surroundings while the inhalation valve closes to prevent flow from the mask back into the bag. All three valves remain closed during the post-expiratory pause while oxygen continues to flow into the reservoir bag.
Inefficiencies in an emergency oxygen supply system can require the oxygen storage or oxygen generation means to be larger and therefore weigh more than necessary which of course has an adverse impact on the payload capacity and fuel consumption of the aircraft. Enhancing the efficiency of such a system either in terms of the generation, storage, distribution or consumption of oxygen could therefore yield a weight savings. Conversely, an enhancement of a system's efficiency without a commensurate downsizing would impart a larger margin of safety in the system's operation. It is therefore highly desirable to enhance the efficiency of an emergency oxygen supply system in any way possible.
An emergency oxygen supply system for use on aircraft in the event of a loss in cabin pressure is configured for delivering allotments of oxygen and timing the delivery such allotments to each passenger so as maximize the efficiency of the transfer of such oxygen into the passenger's bloodstream. The delivery of each allotment is selected so that the entire allotment is available for inhalation into the region of the lung most efficient at oxygen transfer while the volume of the allotment is selected to substantially coincide with the volume of such region of the lung.
The chemical reaction in chemical oxygen generators is exothermic, so that heat released by a chemical oxygen generator needs to be managed in the aircraft installation. Heat can damage nearby aircraft components, and management of the heat adds cost and weight to an aircraft installation.
In March 2011, airworthiness directive (AD) 2011-04-09 was issued by the FAA requiring the removal or disabling of chemical oxygen generators from aircraft lavatories. (see discussion in BEAFS-88039/86205) This AD is in conflict with FAR 25.1447 requiring supplemental emergency oxygen to be available in aircraft lavatories.
It would be desirable to provide an aircraft emergency oxygen dispensing device to dispense supplemental oxygen suitable for breathing generates substantially no heat in operation, and that resolves the conflict between the FAA airworthiness and the regulation requiring supplemental emergency oxygen to be available in aircraft lavatories, by providing a stored source of oxygen as an alternative to chemical oxygen generators for aircraft lavatories.
It would also be desirable to provide such an aircraft emergency oxygen dispensing device that reduces the quantity of oxygen that must be stored, thereby reducing the weight of the system. It would also be desirable to provide such an aircraft emergency oxygen dispensing device that is configured to fit within the dimensional envelope of an existing aircraft oxygen generator, allowing the device to be retrofit as a direct replacement in size, weight and function for an existing aircraft chemical oxygen generator, to reduce or eliminate the need to alter existing installations in aircraft. It would also be desirable to provide such an aircraft emergency oxygen dispensing device that operates substantially in the same manner as an aircraft chemical oxygen generator, and that can be used by an aircraft passenger or crew in the same manner as an aircraft chemical oxygen generator, thereby eliminating the need for additional or new training and explanation by flight crews. The present invention meets these and other needs.